JP3070540B2 - Method for manufacturing compound semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a compound semiconductor device, and more particularly to a method of manufacturing a gate electrode of a MESFET.

[0002]

2. Description of the Related Art A Schottky barrier gate field effect transistor (MESFET) using a group III-V compound semiconductor such as GaAs (gallium arsenide) is formed by contact between a metal and a semiconductor. It has a structure with a junction on the gate electrode, making use of the excellent high-frequency characteristics, low-noise amplifiers for microwave and millimeter-wave bands,
It is often used as a high-power amplifier.

What is important as the gate electrode of the Schottky contact that governs the characteristics and reliability of the MESFET is φ
_B (Schottky barrier height from the metal side) is to be stable and large. For an ideal contact between the metal and the semiconductor, phi _B is given by the difference between the electron affinity χ work function φm and semiconductor metal _{(φ B = φ m -χ)} . Actually, the Fermi level on the surface is pinned by many interface states existing on the surface of the compound semiconductor, and φ _B is determined.

Accordingly, in order to stably increase φ _B , it is desirable that the surface of the semiconductor is as clean as possible and has a low interface state density.

On the other hand, as a gate electrode material, low specific resistance, good adhesion to a semiconductor substrate, low stress,
A metal having heat resistance is desirable. Conventionally, a gate electrode material often used is aluminum (Al). A
1 is because the resistivity is small and a gate electrode of a submicron size can be easily formed by a lift-off method using electron beam evaporation. However, since Al easily causes electromigration, the reliability is significantly reduced as the dimensions are reduced. In recent years, as a highly reliable gate metal material alternative to Al, tungsten (W), molybdenum (Mo), tungsten silicide (WSi _x), tungsten silicide nitride (W
Refractory metal Si _x N _y) and the like have been used.
This refractory metal-based conductive film has the following advantages. First, since the heat resistance is good, a high temperature of 400 to 800 ° C. can be used as a MESFET manufacturing process. Next, since fine processing of a high melting point metal can be performed by dry etching using a halogen gas, a gate metal having a submicron size can be formed. Third, the reliability is high.

GaAsME using refractory metal conductive film
There are three conventional methods for manufacturing SFETs.

FIGS. 4A to 4E are cross-sectional views showing the first example in the order of the steps.

First, as shown in FIG. 4A, an operation layer 2 (channel layer) is formed on a semi-insulating GaAs substrate 1 by epitaxial growth or ion implantation.
A silicon oxide film 3 having a thickness of 400 nm is formed by a PCVD method, a photoresist mask 4-1 is formed using a lithography technique, and the silicon oxide film 3 is selectively dry-etched using an SF ₆ gas to form a gate. An opening 5 for an electrode is formed.

Next, as shown in FIG. 4 (b), a photoresist 4-1 is formed by using a gas containing oxygen (O ₂ ) in a reactor of a barrel type or a parallel plate type for generating a plasma discharge. Is peeled off. As a method for removing a photoresist by a solution, a method of immersing a mixture of dichlorobenzenephenol and alkylbenzenesulfonic acid at a high temperature (120 ° C.) followed by immersion in methyl ethyl ketone and alcohol sequentially (hereinafter referred to as a high-temperature organic agent) Abbreviated as a photoresist stripping method).

Then, as shown in FIG.
The oxide on the GaAs surface and the boride remaining at the time of dry etching are removed by immersion in a hydrochloric acid aqueous solution (the ratio of HCl to H ₂ O is 1: 1), and a gate is formed on the surface of the silicon oxide film including the opening. After forming a WSi film 7 having a thickness of 100 nm to be a part of the electrode by vapor deposition or sputtering,
150 nm thick titanium nitride (TiN) film, 15 n thick
Then, a film (hereinafter abbreviated as TiN-Pt-Au film) 8 is formed by sequentially laminating a platinum (Pt) film having a thickness of m and a gold (Au) film having a thickness of 400 nm by vapor deposition or sputtering.

Next, a photoresist mask (not shown) is formed on the TiN-Pt-Au film 8 by lithography.
And TiN-Pt-Au is formed by ion milling.
After etching the film 8, a reactive ion etching method (hereinafter abbreviated as RIE) using a mixed gas of SF ₆ and CF ₄
The WSi film 7 is dry-etched as shown in FIG.
As shown in FIG. 7, a gate electrode 9-1 is obtained.

Then, as shown in FIG. 4E, the silicon oxide film 2 located at the position where the source electrode and the drain electrode are to be formed is selectively removed, and the source electrode 10 is formed by vapor deposition or sputtering. And a drain electrode 11 are selectively formed to complete a semiconductor device element portion.

Next, a second example of the conventional manufacturing method is shown in FIG.
This will be described with reference to (a) to (e).

First, as shown in FIG.
After a WSi film 7 to be a part of a gate electrode is formed on the GaAs substrate 1 on which is formed by a vapor deposition method or a sputtering method, a TiN-Pt-Au film 8 is formed by a vapor deposition method or a sputtering method.

Next, as shown in FIG.
A photoresist mask 4-2 is formed on the Pt-Au film 8 by a lithography technique, and the photoresist mask 4-2 is formed by ion milling.
After etching the iN-Pt-Au film 7, the WSi film 7 is dry-etched by RIE using SF ₆ gas.

Next, as shown in FIG. 5C, the photoresist 4 is removed by an ashing method using O ₂ gas or a peeling method using a high-temperature organic agent to obtain a gate electrode 9-2.

Next, as shown in FIG. 5D, the GaAs is immersed in an aqueous hydrochloric acid solution (the ratio of HCl to H ₂ O is 1: 1).
After removing the oxide on the s surface and the boride remaining during the dry etching, the insulating film 12 is formed on the entire surface including the gate electrode 9 and the GaAs.

Then, as shown in FIG. 5E, the insulating film 12 located at the position where the source electrode and the drain electrode are formed is selectively removed, and the source electrode 10 and the source electrode 10 are formed by a vapor deposition method or a sputtering method. The drain electrode 11 is selectively formed to complete a semiconductor device element portion.

As a third example of the conventional manufacturing method, Japanese Patent Application Laid-Open No. 9-97913, which aims at removing S remaining on GaAs generated during dry etching, is disclosed in FIGS. 6 (a) to 6 (e). Is disclosed.

First, as shown in FIG. 6A, a channel (operation) layer 2 is formed on a semi-insulating GaAs substrate 1 by epitaxial growth or ion implantation.
A silicon oxide film 3 having a thickness of 400 nm is formed by a CVD method, a photoresist mask 4-1 is formed using a lithography technique, and the silicon oxide film 3 is selectively dry-etched using an SF ₆ gas to form a gate. An opening 5 for an electrode is formed.

Next, as shown in FIG. 6B, after the photoresist is removed by an ashing method using O ₂ gas or a stripping method using a high-temperature organic agent, a hydrochloric acid aqueous solution (HC) is used.
and the H ₂ O ratio is, for example, 1: 1).
After removing the oxide on the surface and the boride remaining during the dry etching, 300 to 6 times in an H ₂ gas atmosphere.
A high temperature bake treatment of less than 00 ° C. is performed.

Then, as shown in FIG. 6C, a 100 nm-thick WSi film 7 serving as a part of the gate electrode was formed on the surface of the silicon oxide film including the opening by vapor deposition or sputtering. After that, titanium nitride (TiN) with a thickness of 150 nm
A TiN / Pt / Au film 8 is formed by sequentially laminating a film, a platinum (Pt) film having a thickness of 15 nm, and a gold (Au) film having a thickness of 400 nm by a vapor deposition method or a sputtering method.

Next, as shown in FIG.
A photoresist mask is formed on the Pt / Au film 8 by using a lithography technique, and Ti is formed by ion milling.
After etching the N.Pt.Au film 8, SF ₆ and CF
_The WSi film 7 is dry-etched by RIE using the mixed gas of ₄ to obtain the gate electrode 9-1.

Then, as shown in FIG. 6E, the silicon oxide film 3 located at the position where the source electrode and the drain electrode are to be formed is selectively removed, and the source electrode 10 is formed by vapor deposition or sputtering. And a drain electrode 11 are selectively formed to form a semiconductor device element portion.

[0025]

In the first example of the conventional method for manufacturing a compound semiconductor device described above, when dry etching a silicon oxide film to form an opening for a gate electrode, an SF ₆ gas is used. Therefore, there is a problem that residual sulfur 6 (residue made of sulfur or its compound) exists on the GaAs surface at the gate electrode opening. Similarly, in the second example of the conventional manufacturing method, since the WSi film is dry-etched using SF ₆ gas, the residue made of S is G
There was a problem that remained on the aAs surface. If residual sulfur is present on the GaAs surface, the sulfur is doped into the GaAs, forming a gate metal on the GaAs surface.
Since φ _B between the gate metal and GaAs is reduced, there is a problem that the FET characteristics are deteriorated along with the Schottky characteristics. This problem is already known, and in 1996,
IEICE Technical Report Vol. 96 No. 353, 27 "Ga
Gate Leakage Current Generation Mechanism in AsHIGFET "
Has been reported.

In the third example, a normal temperature hydrochloric acid aqueous solution treatment is performed after dry etching with SF ₆ gas,
_This shows a method of removing residual sulfur by performing a high-temperature bake treatment at 300 to 600 ° C. in a _two- gas atmosphere. However, it has been desired to lower the temperature of the treatment and shorten the process. Further, there is a possibility that hydrogen may enter the semiconductor layer and change device characteristics.

Although dry etching can be performed by using CHF ₃ or CF ₄ gas without using SF ₆ gas, the etching damage to the GaAs substrate becomes larger than when SF ₆ is used. However, there is a problem that the FET characteristics cannot be stably obtained.

In view of the above, it is an object of the present invention to provide a method of manufacturing a compound semiconductor capable of removing S residues generated during dry etching for forming a gate electrode and reducing dry etching damage. .

[0029]

According to a method of manufacturing a compound semiconductor device of the present invention, a gas containing at least sulfur is formed on a compound semiconductor substrate having an operation layer formed on one principal surface and a first film formed on the operation layer. A first step of selectively removing the first film by performing dry etching using a method and exposing a surface of the operation layer; and performing a hot hydrochloric acid treatment at 50 ° C. or higher after the first step. Performing a second step of removing residual sulfur from the exposed surface of the operation layer. The present invention prevents the Schottky barrier height of the gate electrode forming the Schottky junction with the operation layer from being reduced by the residual sulfur. If the compound semiconductor substrate is a GaAs substrate, the temperature of the hot hydrochloric acid aqueous solution is preferably 50 to 98 ° C., and the HCl concentration in the hot hydrochloric acid aqueous solution is preferably 9.3%.

In the method of manufacturing a compound semiconductor according to the present invention, an insulating film can be formed as the first film, and a second film forming a Schottky junction with the operating layer can be deposited after the second step. In this case, a film made of a high melting point metal or a compound thereof can be used as the second film.

Further, a conductive film forming a Schottky junction with the operation layer can be formed as the first film. In this case, a film made of a high melting point metal or a compound thereof can be used as the conductive film. In all of the above cases, dry etching using SF ₆ gas can be performed.

[0032]

Embodiments of the present invention will now be described with reference to the drawings. FIGS. 1A to 1E are cross-sectional views of a semiconductor device shown in the order of steps for describing an embodiment of the present invention.

The insulating film 3 or the first film made of the refractory metal film on the GaAs substrate 1 having the operation layer 2 is dry-etched using SF ₆ gas. At this time, GaAs
Residual sulfur 6 remains on the surface (see FIG. 1A). Next, the photoresist 4-1 is removed, and the remaining sulfur 6 is removed by immersion treatment in a hot hydrochloric acid aqueous solution of 50 to 98 ° C. (see FIG. 1B). Then, a gate electrode is formed (see FIGS. 1C and 1D), and a source / drain electrode is formed to obtain a semiconductor device (FIG. 1E).

Example 1 An example of the above embodiment will be described below in detail with reference to FIG.

First, as shown in FIG. 1A, after an operation layer 2 is formed on the surface of a semi-insulating GaAs substrate 1 by epitaxial growth or ion implantation, a 400 nm-thick silicon oxide film 3 is formed by LPCVD. Form a film.
In addition, instead of the silicon oxide film 3, silicon nitride (Si
N _x ) film or silicon oxynitride (SiO _x N _y ) film. Next, after a photoresist mask 4-1 is formed by using a lithography technique, the silicon oxide film is selectively dry-etched using SF ₆ gas to form an opening 5 for forming a gate electrode. At this time, residual sulfur 6 (residue consisting of sulfur or its compound) remains on the GaAs surface.

Next, as shown in FIG. 1B, an ashing method using a gas containing oxygen or a high-temperature (120 ° C.) After dipping in a mixed solution of dichlorobenzene phenol and alkylbenzene sulfonic acid, the photoresist mask 4 is removed by a method of dipping in methyl ethyl ketone and alcohol sequentially. HCl is immersed in a hot hydrochloric acid aqueous solution containing 17.2% of concentrated hydrochloric acid (hereinafter abbreviated as conc. HCl) containing 17.2% HCl at a temperature of 70 ° C., and oxides on the GaAs surface and residues during dry etching. Fluoride and residual sulfur 6 are removed. Thereby, a clean GaAs surface is obtained. Note that the temperature of the hot hydrochloric acid aqueous solution at this time is desirably 50 to 98 ° C. This is 50
If the temperature is lower than 98 ° C., the removal of residual sulfur becomes insufficient, and if the temperature is higher than 98 ° C., the GaAs surface becomes rough. Further, the HCl concentration of the hot hydrochloric acid aqueous solution is preferably 9.3% or more, and conc. HCl may be used. Here, if the concentration is less than 9.3%, the removal of residual sulfur is insufficient.

Next, as shown in FIG. 1C, a WSi film serving as a part of the gate electrode is formed on the surface of the silicon oxide film including the opening.
The film 7 is formed to a thickness of 100 nm by an evaporation method or a sputtering method. At this time, it is desirable to form a film within 30 minutes immediately after immersion in hot hydrochloric acid. Next, a 150-nm-thick titanium nitride film, a 15-nm-thick platinum film, and a 400-nm-thick gold (A
u) A TiN-Pt-Au film 8 in which films are sequentially stacked is formed by a vapor deposition method or a sputtering method. Next, TiN-
A photoresist mask (not shown) is formed on the Pt-Au film by a lithography technique, the TiN-Pt-Au film 8 is etched by an ion milling method, and then reactive ion etching using a mixed gas of SF ₆ and CF ₄ is performed. The dry etching of the WSi film 7 by the method shown in FIG.
A gate electrode 9 as shown in FIG.

Next, as shown in FIG. 1E, the silicon oxide film 3 located at the position where the source electrode and the drain electrode are to be formed is selectively removed, and the source electrode 10 and the drain electrode 11 are formed by an evaporation method. Alternatively, a semiconductor device element portion is formed selectively by a sputtering method.

The SIMS analysis (2) shows that the treatment with hot hydrochloric acid reduces the residual sulfide at the bonding surface between GaAs and WSi as compared with the treatment with hydrochloric acid at room temperature.
Secondary ion mass spectrometry). After dry etching, perform normal temperature hydrochloric acid treatment or hot hydrochloric acid treatment,
SIMS on GaAs surface with WSi gate metal
The result of the analysis is shown in FIG. By performing the hot hydrochloric acid treatment, the number of detected S is reduced by about one digit compared with the case of the normal temperature hydrochloric acid treatment. GaAsM manufactured by performing the hot hydrochloric acid treatment of the present embodiment
It has been confirmed that the gate withstand voltage BVgd is improved and the gate leakage current Igd is reduced in the ESFET. B in a 100 μm gate width MESFET treated with hydrochloric acid at room temperature
The average of Vgd is 5.0 V and the average Igd is 0.5 μA, but the average of BVgd is 5.7 V and the average Igd is 0.2 μA in the device subjected to the hot hydrochloric acid treatment.

That is, the opening for forming the gate electrode is
Since the active layer is formed by RIE using F6, damage to the active layer is small, and the residual sulfur remaining on the active layer of the compound semiconductor is efficiently removed by hot hydrochloric acid treatment. Gate electrode having a low level can be formed stably. Therefore, it is possible to improve the gate leak and the low breakdown voltage of the MESFET.

Embodiment 2 FIGS. 2A to 2E are cross-sectional views of a semiconductor device for explaining a second embodiment in the order of steps.

As shown in FIG. 2A, a 1000 nm-thick WSi film 7 serving as a part of a gate electrode was formed on a GaAs substrate 1 on which an operation layer 2 was formed by vapor deposition or sputtering. Thereafter, a TiN-Pt-Au film 8 is formed by an evaporation method or a sputtering method. Next, as shown in FIG. 2B, a photoresist mask 4 is formed on the TiN-Pt-Au film 8 using a lithography technique, and the TiN-Pt-Au film 8 is etched by an ion milling method.
The WSi film 7 is dry-etched by a reactive ion etching method using a mixed gas of SF ₆ and CF ₄ . At this time, residual sulfur 6 remains on the GaAs surface. Next, an ashing method using a gas containing oxygen or a high-temperature (120 ° C.) dichlorobenzene phenol and an alkylbenzene sulfone is applied to the photoresist mask 4 in a reaction vessel that generates plasma discharge such as a barrel type or a parallel plate type. after immersed in a mixed solution of the acid, methyl ethyl ketone, after removal by a method of sequentially immersing in alcohol, hot hydrochloric acid aqueous solution (e.g., a ratio of conc.HCl and H ₂ O is 1:
1 and a temperature of 70 ° C.) to remove residual sulfur 6 on the GaAs surface, thereby obtaining a clean GaAs surface and a gate electrode as shown in FIG. 2C.

Next, as shown in FIG. 2D, an insulating film 12 is formed on the gate electrode and the GaAs layer 2.

Next, as shown in FIG. 2E, the insulating film 12 located at the place where the source electrode and the drain electrode are to be formed is selectively removed, and the source electrode 10 and the drain electrode 11 are formed by vapor deposition or sputtering. A semiconductor device element portion is formed selectively by a method. Since residual sulfur can be removed from around the junction of the gate electrode, abnormalities in the Schottky characteristics around the gate electrode can be suppressed.

The gate electrode WSi film 7 and the GaAs substrate 2
The residual sulfur is removed from the periphery of the Schottky junction with the Schottky barrier, so the Schottky barrier height φ around the gate electrode
_B can be suppressed from decreasing. Therefore, the gate leakage and low breakdown voltage of the MESFET can be improved as compared with the conventional manufacturing method.

As described above, in the first and second embodiments, the gas of SF ₆ alone was used, but other gases may be mixed. Also SF ₆
Any gas may be used as long as it is a compound or a mixture having S and F, such as S ₂ F ₁₀ , instead of S.

In the first and second embodiments, Ga is used as the operation layer.
Although an As layer was used, an AlGaAs layer may be used.

In addition to a semiconductor device using a GaAs substrate, a semiconductor substrate of another group III-V, for example, In
A P substrate or the like may be used.

According to the present invention described above, after a gate opening or a gate electrode is formed by dry etching using a sulfur-containing gas such as SF ₆ gas, residual sulfur remaining in an operation layer on a compound semiconductor substrate is formed. Can be easily removed by hot hydrochloric acid treatment, so that a clean semiconductor surface can be obtained. Moreover, since ion etching using a gas containing carbon is not used, dry etching damage can be reduced.
Therefore, a gate electrode having a constantly stable φB and a gate electrode having a constantly stable Schottky characteristic can be formed, and the gate leakage current and the mutual conductance of the MESFET can be improved.

Further, not only the residue does not exist at the interface between the gate electrode and the semiconductor, but also the stoichiometry at the interface is improved, so that the reliability of the semiconductor device is improved.

[Brief description of the drawings]

FIGS. 1A to 1E are cross-sectional views in the order of steps for explaining a first embodiment of the present invention.

FIG. 2 is a graph illustrating the result of SIMS analysis of a GaAs / WSi interface using a hot hydrochloric acid treatment according to an embodiment of the present invention and a case using a room temperature hydrochloric acid treatment for explaining the first embodiment. FIG.

FIGS. 3A to 3E are cross-sectional views in the order of steps, for illustrating a second embodiment of the present invention.

FIGS. 4A to 4E are cross-sectional views illustrating a first example of a conventional method for manufacturing a compound semiconductor device in the order of steps.

5A to 5E are cross-sectional views in the order of steps for explaining a second example of the conventional method for manufacturing a compound semiconductor device.

6A to 6E are cross-sectional views in the order of steps for explaining a third example of the conventional method for manufacturing a compound semiconductor device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 GaAs substrate 2 Operating layer (channel layer) 3 Silicon oxide film 4-1 and 4-2 Photoresist mask 5 Opening 6 Residual sulfur 7, 7a, 7b WSi film 8, 8a, 8b TiN-Pt-Au film 9-1 , 9-2 Gate electrode 10 Source electrode 11 Drain electrode 12 Insulating film

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 29/812 H01L 29/872 H01L 21/338 H01L 21/28 H01L 21/3065

Claims (8)

(57) [Claims] 1. An operation layer on one main surface and a first layer on the operation layer.
A first step of selectively removing the first film by performing dry etching using a gas containing at least sulfur (S) on the compound semiconductor substrate formed with the film and exposing the surface of the operation layer And after the first step, 50
A method of manufacturing a compound semiconductor device, comprising a second step of removing residual sulfur from an exposed surface of the operation layer by performing a treatment with hot hydrochloric acid at a temperature of not less than ° C. 2. The method for manufacturing a compound semiconductor device according to claim 1, wherein the compound semiconductor substrate is a GaAs substrate, and the treatment is performed with a hydrochloric acid aqueous solution having a temperature of 50 ° C. or more and less than 98 ° C. and an HCl concentration of 9.3% or more. 3. The method according to claim 1, wherein the operation layer is GaAs or AlGaAs.
3. The method for manufacturing a compound semiconductor device according to claim 1, wherein 4. The method according to claim 1, further comprising a step of forming an insulating film as the first film, and depositing a second film forming a Schottky junction with the operation layer after the second step. Or a method for manufacturing a compound semiconductor device according to item 3. 5. The method according to claim 4, wherein the second film is made of a high melting point metal or a compound thereof. 6. The method according to claim 1, wherein a conductive film forming a Schottky junction with the operation layer is formed as the first film. 7. The method of manufacturing a compound semiconductor device according to claim 6, wherein said conductive film is made of a high melting point metal or a compound thereof. 8. The method for manufacturing a compound semiconductor device according to claim 1, wherein said gas containing sulfur is SF ₆ gas.